The present invention relates to a lubricant doser comprising a body having a dosing cylinder and a dosing piston moving axially therein, and means for leading lubricant alternately to both sides of the dosing piston.
It is previously well known in the field to lubricate a plurality of lubrication points using a common fixed lubricant source. In this kind of centered lubrication system, a sufficient number of dosers is installed in the vicinity of the lubrication points, one doser usually servicing two lubrication points. The dosers are connected with pipes to a pump that feeds the lubricant to the dosers at intervals determined by a control unit, the dosers each dispensing a desired quantity of the lubricant, as directed, and pressing each lubricant dose to the lubrication point. A control valve in each doser leads the lubricant dispensed by the respective dosing piston to both respective lubrication points in turn.
Most of the previously known central lubrication systems include two pipes, each of the dosers being connected to the pump with two body pipes through which the lubricant is fed to each doser in turn. The movements of the control valve, which are essential for leading the lubricant dose alternately to different lubrication points, are thereby effected by alternate pressurization of the body pipes in such a way that the pressure in one body pipe pushes the control valve to another position and the pressure in the other body pipe pushes the control valve back. A drawback in this kind of system is that two pipes must be installed between the pump and the dosers. However, such double piping is expensive and more complicated to install.
To eliminate this drawback, dosers have been developed that can be connected to the pump with one body pipe, whereby any drawbacks of double piping are eliminated. An example of dosers and systems of this kind is provided by the solution described in Finnish Patent 66,978. A drawback in the above solution is, however, that it cannot be quite well applied to all lubricants. Problems may occur with difficult greases, i.e. greases in which oil and soap tend to separate. Another drawback is e.g. insufficient pressurization of one side of the doser caused by a difference in the surface area of the control valve.